The Ramsay-Graham heterogeneous simple shear zone model revolutionized our understanding of finite strain variation in orogenic belts. Many deeply exhumed (>20 km depths) shear zones in orogenic continental crust are a consequence of sub-simple shear strain accumulation during contraction and displacement at high temperature. Here we explore the micro-scale record of this process using syn-kinematic monazite in two shear zones in a >20,000 km² terrane of exhumed lower continental crust. Field observations combined with high-spatial resolution X-ray mapping, Th–U-Pb electron microprobe petrochronology, and electron backscatter diffraction analysis demonstrate that monazite grains can provide an important textural and temporal record of shear strain in mylonite and ultramylonite gneisses. Monazite grains exhibit aspect ratios of 1.7–4.6 parallel to the stretching lineation and parallel or oblique (<30°) to the penetrative foliation. Monazite EBSD data for grain orientation spread, i.e., average misorientation relative to the mean, are consistent with no significant dislocation-accommodated internal deformation. We conclude that dissolution precipitation creep of monazite produced compositionally-defined geometries compatible with the dextral sense of shear observed in outcrop and thin section. Syn-kinematic rims on monazite grains that develop in low strain domains during accumulation of shear strain can provide absolute ages for μm-to km-scale kinematics in continental orogens.

Ramsay-Graham 非均质简单剪切带模型彻底改变了我们对造山带有限应变变化的理解。造山大陆地壳中许多深挖出（>20 km 深度）的剪切带是高温收缩和位移过程中亚简单剪切应变积累的结果。^{在这里，我们在 >20,000 km 2}的两个剪切带中使用同运动独居石探索了这一过程的微观记录出土的下大陆地壳地体。现场观测与高空间分辨率 X 射线测绘、Th-U-Pb 电子探针岩石年代学和电子背散射衍射分析相结合，表明独居石颗粒可以提供糜棱岩和超糜棱片麻岩中剪切应变的重要纹理和时间记录。独居石晶粒的纵横比为 1.7-4.6，平行于拉伸线，平行或倾斜 (<30°) 穿透叶理。晶粒取向扩展的独居石EBSD 数据，即相对于平均值的平均取向错误，与没有明显的位错调节的内部变形一致。我们得出结论，独居石的溶解沉淀蠕变产生了与在露头和薄片中观察到的右旋剪切感相一致的成分定义的几何形状。在剪切应变积累过程中，在低应变域中形成的独居石晶粒上的同步运动边缘可以为大陆造山带中微米到公里尺度的运动学提供绝对年龄。